1. Field of the Invention
The present invention relates to an endoscope, and particularly, to a small-sized endoscope that performs observation, surgery, or the like of a constricted part in the medical field or the industrial field.
2. Description of the Related Art
In the related art, in the medical field or the industrial field, endoscopes for imaging the interior of a patient's body or the inside of a device or a structure have spread. In these types of endoscopes, there is known a configuration in which, in an insert section inserted into the inside of an object to be observed, the light from an object to be imaged is image-formed on a light-receiving surface of an image pickup device by an objective lens systems, and the image-formed light is converted into electrical signals and the converted electrical signals are transmitted to an external image processing device or the like as video signals via a signal cable.
A number of parts, such as optical elements, such as an image pickup device and a lens that focuses a light image on an imaging surface of the image pickup device, are arranged in a distal end portion provided at the distal end of the insert section of these types of endoscopes. There is known a configuration in which an imaging direction, that is, a visual field, is changed on the basis of the operation of a surgeon or the like by connecting the distal end portion to a linear hard part on a rear end side of the insert section via a bendable bending portion. In recent years, in the endoscopes having a complicated configuration in this way, in order to perform simpler manufacturing and to alleviate a patient's burden, further diameter reduction of the external diameter has been important.
For example, Japanese Patent Unexamined Publication No. 7-327916 discloses a visual-field direction change type endoscope that includes visual-field conversion means that causes some of rays, which are incident from a transparent window arranged from a distal end surface of a distal end of an insert section to the middle of a side portion near the distal end, to selectively enter an objective optical system of a rotationally provided imaging unit and to fall within a visual field range, and that can freely switch the direction of the visual field of the endoscope according to the applications thereof or an object to be observed.
Japanese Patent Unexamined Publication No. 2012-50704 discloses an electronic endoscope in which a space for installing an imaging module including an image pickup device is provided inside a distal end portion of the endoscope, the inside of a metal frame including the imaging module is filled with isotropic high heat conduction resin, and a space around the metal frame is filled with anisotropic high heat conduction resin having a higher thermal conductivity in the direction of an outer peripheral portion of the endoscope than that in a longitudinal direction of the endoscope.
In the endoscope having the configuration in which the imaging unit including the image pickup device is arranged at the distal end portion as described above, a countermeasure against dissipation of the heat generated in the image pickup device becomes a challenge. Particularly when the endoscopes are used in the medical field, heat dissipation of a distal end portion is required in order to suppress the temperature of the endoscope insert section within a human's body that is a photographic subject with the suppression of performance deterioration, such as an increase in noise caused by heat generation.
When a low-resolution image pickup device is used, heat is not generated so much. Therefore, this does not become a problem. However, when a high-resolution image pickup device is used, the heat generation in the image pickup device is large in the related art. Therefore, a heat dissipation structure of the distal end portion is required. In the endoscope including the high heat conduction resin and a tubular body as the heat dissipation structure of the distal end portion in which the imaging unit is arranged as in the related-art example described in Japanese Patent Unexamined Publication No. 2012-50704, the diameter of the distal end portion becomes large, and there is a problem in that bending becomes difficult.